Obama Has Few Options to Challenge Russia on Ukraine

U.S. Administration Shifts to Sterner Tone With Moscow, Voicing Concern on Military Moves

Updated Feb. 28, 2014 8:40 p.m. ET

WASHINGTON—Until Friday, the American approach to Ukraine's mounting crisis was designed explicitly to show the U.S. didn't view this as a return of Cold War frictions, but as an opportunity to work with Moscow to stabilize a former Soviet state.

That changed late in the day when President Barack Obama bluntly warned Russia against intervening in Ukraine, a stark indication that old tensions are seeping back into the...